Terence Blacker: The planet will be saved on the playing fields of Eton

At first glance, it might have been any other gathering of well-heeled toffs and debs. There were Range Rovers, Mercedes and Volvo estates parked in a field behind the big house. Young people, with that rosy complexion and thick hair that privilege seems to bring, were making their way up the stone steps in evening dress, chattering like starlings. In the hall, our hosts the Honourable Rory and Serena Bass-Withers were greeting us as we arrived.

In another age, it might have been a hunt ball or a coming-out dance, but we live in troubled times when Planet Earth needs all the help we can get and environmentalism is all the rage. This was one of the new Green Balls which are popular among the rural party-going set and are finding their way into the pages of the Tatler and Country Life.

"There's nothing odd about our sort of people being green," Serena Bass-Withers told me over a glass of champagne. "I can't think why people should be surprised that David Cameron and Zac Goldsmith are frightfully keen on global warming and all that stuff. In a sense, people like us started it all, with our green wellies, our green Barbours and green Land Rovers. The rest of the world has caught up and now it's quite the thing to be doing something rather sustainable or renewable."

All the same, I admitted to being surprised to find this level of environmental commitment in the deb-dance set. Where had it all started, I wondered.

"Eton," said the Honourable Rory, rather surprisingly. "They drummed the old eco-stuff into Zac and David when they were there and now they're doing it to our boy Jeremy. Whenever we're about to fly to Gstaad or Mustique, the little chap pipes up with an awkward question about the carbon footprint. I promise that we'll do something green when I get home. I bought Gibbett the gamekeeper an electric car the other day - he wasn't thrilled but I told him he had to set an example. It's the way people like us respond to environmental challenges that will show ordinary folk how serious the situation is."

"We've put up a windmill, haven't we, darling?" said Serena.

"Exactly. We wanted to show the world that we weren't one of those not-in-my-back-yard johnnies, so we bought our very own turbine. Not that one actually put it up in a back yard - we don't do back yards on the estate - but it's in the Low Meadow, beyond the big wood. I think the point was made."

We wandered through to the dining-room where the Green Ball guests would be eating later. "Everything we're serving is really organic," Serena told me. "I'm very strict about that. Even if something is being flown in from South Africa or New Zealand, I always ask what I call my key questions. Is it organic? And is it sustainable?"

"What's more, all the pheasants which we'll be eating tonight are environmentally friendly," the Honourable Rory added. "Bred here on the estate by Gibbett. Released a couple of months ago. Shot by weekend shooting parties. Eaten within a mile or so of where they were first incubated. It's a small thing perhaps, but it symbolises practical, everyday eco-thinking in action. Everybody gains - except perhaps the pheasants."

It was an inspiring example to us all, I said. But how would this new green attitude to life reach the wider world?

"All I can say is we're doing our bit as ordinary country folk," said Serena. "We insist that low-energy light-bulbs are used in the staff quarters. My friends who have babies tell their nannies to wash cloth nappies rather than using the disposable type. When I drive to London to have my hair done, I always use my little BMW rather the Range Rover. Actions not words are the thing when it comes to the green lifestyle."

I left Serena and Rory to wander among their guests. How exciting it was, I thought, that the environment had become so fashionable and socially OK. As I drank my champagne and nibbled at an organic quail's egg, the future of the world suddenly seemed a little more hopeful.

Miles Kington is away